The function counts the number of occurrences of the word "world" in a given input string (case sensitive) and returns the count as a word.

[CODE]: 
```python
def f(string):
    count = string.count("world")
    word_count = ["zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine"]
    return word_count[count]
```